Assembling an electric bell on an electrical board
Before assembling the electric bell, the diagram and the parts (electromagnet, armature hammer, gong, contact screw, switch, battery, connecting wires) are checked. Order: 1) fix the electromagnet firmly on the board with a screw; 2) attach the elastic armature plate to the electromagnet end leaving a 1–2 mm gap; 3) fit the hammer to the armature and the gong where the hammer hits it; 4) fix the contact screw so that it lightly touches the armature plate; 5) wire the circuit as in the diagram: battery – switch – contact screw – armature – coil – battery; 6) show the connections to the teacher; 7) test by pressing the switch briefly. If the bell does not ring, look for the fault: is the battery low, are the ends well connected, does the contact screw touch the armature, and what is the gap between armature and core. The circuit is powered only from a battery up to 4.5 V. Disconnect the battery before changing connections. Soldering is done by the teacher; pupils work only with screw terminals. Wire ends must be clean and not touch each other: in a short circuit the battery drains fast and the wire heats.
Fault finding: the teacher hands out 3 bell models deliberately misadjusted (loose end, loose screw, weak battery). Groups check causes in order, write them in a table and fix them. Only batteries are used.